5.1 Strengthen Questions
Key Takeaways
- Strengthen questions ask for the answer choice that, if assumed true, provides the strongest logical support for the conclusion.
- The correct choice does not need to prove the conclusion with 100% certainty; it only needs to increase the probability or plausibility of the conclusion.
- For causal arguments, strengthening involves eliminating alternative causes, showing cause without effect is absent, showing cause present leads to effect, or establishing data reliability.
- Effective strengtheners bridge the unstated gap between stated premises and the conclusion by validating an implicit necessary assumption.
- Common wrong answer traps include weakeners, statements that support a different conclusion (shell games), and choices that merely restate existing premises.
Understanding Strengthen Questions
Strengthen questions are one of the most frequently tested task types on the LSAT Logical Reasoning section. They evaluate your ability to identify evidence that bolsters an argument's conclusion. The question stem typically asks you to accept the information in each answer choice as true and determine which choice provides the strongest support for the argument.
Common question stem phrasings include:
- "Which one of the following, if true, most strengthens the argument?"
- "Which one of the following, if assumed true, provides the most support for the executive's conclusion?"
- "Which one of the following, if true, does the most to justify the reasoning above?"
The "If Assumed True" Constraint
A critical rule for Strengthen questions is contained within the phrase "if true" or "if assumed true." This phrase means you must grant the factual truth of whatever statement appears in the answer choice, regardless of how surprising, novel, or real-world improbable it might sound. Your objective is not to evaluate whether the answer choice itself is plausible in daily life, but rather to assess the impact the choice would have on the author's argument if it were established as fact.
The Architecture of Strengthening
To strengthen an argument effectively, you must first isolate its argument core: the premises (the evidence provided) and the conclusion (the claim being established). Most LSAT arguments suffer from an argumentative gap—an unstated assumption or logical leap between the premises and the conclusion. A premise does not fully guarantee the conclusion; there is room for doubt.
[ Premise / Evidence ] + [ Missing Bridge / Strengthener ] ---> [ Conclusion (Higher Probability) ]
Degree of Support Required
Unlike Sufficient Assumption questions—which require an answer choice to render the conclusion 100% logically bulletproof—Strengthen questions only require an answer choice that makes the conclusion more likely to be valid than it was before. Even a modest incremental increase in probability is sufficient, provided it does more work than any of the other four options.
Causal Strengthening Mechanics
Causal reasoning is the single most common argument structure on the LSAT. In a causal argument, the author observes a correlation or sequence of events in the premises and jumps to the conclusion that one event caused another (Cause $\rightarrow$ Effect).
When an author claims that $X$ caused $Y$, the argument implicitly assumes that nothing else caused $Y$, that $Y$ did not cause $X$, and that the data observing $X$ and $Y$ is accurate. Consequently, there are five classic, standardized ways to strengthen a causal claim on the LSAT:
| Method | How it Strengthens the Causal Argument | Real-World / Exam Example |
|---|---|---|
| 1. Eliminate Alternative Causes | Shows that another plausible factor ($Z$) was not responsible for the effect ($Y$). | Proving that patient health improved without dietary changes, ruling out diet as the cause. |
| 2. Cause Present $\rightarrow$ Effect Present | Shows another case where the cause occurs and the effect also occurs. | Showing that a second hospital using the same hygiene routine also reduced infection rates. |
| 3. Cause Absent $\rightarrow$ Effect Absent | Shows a control case where the cause is removed and the effect disappears. | Demonstrating that when the new teaching method was removed, test scores returned to baseline. |
| 4. Eliminate Reverse Causation | Proves that the alleged effect did not actually precede or cause the alleged cause. | Demonstrating that psychological distress existed prior to the onset of insomnia, not after. |
| 5. Validate Data Integrity | Confirms that the study, survey, or measurement instruments were non-biased and accurate. | Verifying that temperature sensors used in a climate study were properly calibrated. |
Non-Causal Strengthening Patterns
While causal arguments dominate, Strengthen questions also frequently feature non-causal reasoning structures:
1. Plan and Policy Arguments
When an argument proposes a plan to achieve a specific goal, strengthening the argument involves showing that the plan is feasible, will actually achieve the desired outcome, or lacks fatal side effects that would undermine the goal.
2. Statistical and Sampling Arguments
When an argument relies on a sample or survey to reach a broad conclusion, strengthening the argument involves establishing that the sample was representative, unbiased, sufficiently large, and properly conducted.
3. Arguments by Analogy
When an author argues that because Situation A had Outcome X, Situation B will also have Outcome X, strengthening the argument involves establishing key similarities between A and B or showing that relevant differences do not exist.
Step-by-Step Tactical Method
- Analyze the Question Stem First: Confirm that the stem asks for a strengthener and note any specific focus (e.g., "strengthens the hypothesis regarding bird migration").
- Identify the Core: Explicitly state the premise(s) and conclusion. Locate the exact leap in logic.
- Prephrase the Strengthening Function: Ask yourself: "What missing piece of information would make this conclusion much more convincing?" If it is a causal argument, scan for alternative causes to eliminate.
- Evaluate Answers Against the Prephrase: Test each choice by asking: "If I accept this as true, does it increase the likelihood that the conclusion is correct?"
Common Wrong Answer Traps
- The Opposite Choice (Weakener): Casts doubt on the conclusion rather than supporting it. Test-takers often misread the stem or argument direction and fall for this trap.
- The Shell Game / Out of Scope: Supports a statement that sounds similar to the conclusion, but actually relates to a different topic, population, or timeframe.
- Restating a Stated Premise: Repeats information already given in the stimulus. While true, it adds zero net support to the argument's inference gap.
- Irrelevant True Statements: Provides factual information that is interesting or true in the real world but has no logical connection to the specific conclusion drawn.
A recent study observed that city residents who regularly visit public parks report lower stress levels than residents who rarely visit parks. The researchers concluded that spending time in public parks directly causes reductions in psychological stress. Which one of the following, if true, most strengthens the researchers' argument?
To reduce municipal water consumption during severe droughts, the city council plans to subsidize low-flow toilet installations for all residential homeowners. The council reasons that because residential toilet flushing accounts for 30 percent of total municipal water usage, this subsidy will successfully reduce overall municipal water consumption. Which one of the following, if true, most strengthens the city council's argument?
A historian argues that a newly discovered 14th-century manuscript was authored by Geoffrey Chaucer. The historian bases this conclusion on the observation that the manuscript uses several archaic vocabulary words that appear exclusively in Chaucer's known works from that decade. Which one of the following, if true, most strengthens the historian's argument?
An agricultural researcher claims that applying organic compost to wheat fields yields higher crop volumes than applying synthetic chemical fertilizers. To support this, the researcher notes that fields treated with organic compost produced 15 percent more wheat per acre over a three-year trial. Which one of the following, if true, most strengthens the researcher's argument?